1. Field of the Invention
This invention relates to auxiliary stabilizers for an aqueous suspension of synthetic zeolite A, to a process for producing this suspension on an industrial scale and to the use of the suspension for the production of low-phosphate and phosphate-free detergent powders and cleaners.
2. Statement of the Related Art
The use of synthetic zeolites of the A type, particularly zeolite NaA, as a builder in detergents and as a substitute for sodium tripolyphosphate in detergents and cleaners has acquired increasing significance in recent years. Thus, numerous zeolite-containing detergents based on low-phosphate and phosphate-free formulations have already appeared on the market. Moreover, the use of zeolite A as a new water-insoluble detergent ingredient on a commercial scale has also resulted in new developments in detergent technology. In this connection, special mention may be made of the processing of zeolite A in the form of a storable, free-flowing suspension of very high zeolite content. (For the production of zeolite-containing detergents, particularly using stabilized zeolite suspensions, see O. Koch, Seifen-Oele-Fette-Wachse, 106 (1980), pages 321 to 324).
The stabilization of zeolite suspensions which are still free-flowing, even after storage and transport, and which may be stirred and pumped through pipes and also the use of suspensions such as these for the production of detergent powders are known from U.S. Pat. No. 4,072,622 and its divisionals U.S. Pat. Nos. 4,169,075 and 4,438,012, as well as corresponding Canadian Pat. No. 1,071,058 and German patent application No. 25 27 388. A series of six different classes of organic and inorganic compounds have been proposed as stabilizers, including certain substantially insoluble nonionic surfactants. U.S. Pat. No. 4,179,393 and its divisional U.S. Pat. No. 4,264,480, as well as corresponding Canadian Pat. No. 1,084,802 and German patent application No. 27 02 979, recommend certain adducts of amines or glycols with alkylene oxides as stabilizers for aqueous zeolite suspensions. According to the teaching of German patent application No. 26 15 698, the stabilizers according to above-mentioned German patent application No. 25 27 388 are used in conjunction with a stabilizer auxiliary selected from the group comprising non-surface-active, organic and inorganic water soluble salts having molecular weights below 1000, such as sodium sulfate, sodium citrate, sodium tripolyphosphate, sodium carbonate, etc. This provides for greater flexibility in adapting the viscosity of the suspensions to the storage and processing conditions.
In view of the increasing interest being shown by the detergent industry in the use of zeolites instead of triphosphate as a detergent builder, many other proposals have been put forward regarding the production and composition of stabilized aqueous zeolite suspensions. Thus, German patent application No. 28 54 484 (and corresponding European patent application No. 12,346); British patent application No. 2,048,841 (and corresponding German patent application No. 30 16 433); and British patent application No. 2,053,880 (and corresponding German patent application No. 30 26 511); all describe polymeric compounds of very high molecular weight, of the acrylamide/acrylic acid copolymer of ethyl acrylate/methacrylic acid copolymer type, as stabilizers for aqueous zeolite suspensions. Stabilizers based on phosphoric acid mono- or diesters of fatty alcohol ethoxylates are known from German patent application No. 30 30 955. In addition, the use of certain organic and inorganic water soluble salts as stabilizers either on their own or in conjunction with nonionic surfactants is known from a number of publications. Thus, German patent application No. 30 21 295 recommends the use of sodium nitrilotriacetate. On the other hand, water glass solutions, gel-like aluminium oxides or silicon oxides, soaps having a chain length of C.sub.5 to C.sub.22 and sodium salts of the washing alkali type, including sodium hydroxide, are proposed in Japanese patent application Nos. 54/64,504; 55/127,499; 57/34,017; 57/61,615; and 57/67,697.
The requirements which the properties of zeolite suspensions have to satisfy depend to a certain extent on the type of detergents and cleaners in whose production they are to be used. It has been found, however, that if they are to be useable on an industrial scale, the zeolite suspensions must have the following individual properties: stability over a wide temperature range extending from room temperature or lower to at least 70.degree. C.; any sediment formed after prolonged storage must be redispersible by means of stirrers; viscosity should remain low, even at low temperatures, to guarantee stirrability and pumpability; and when the stabilizers zers are incorporated, they should neither dilute the suspension nor affect the pH in any way. Finally, the suspension stabilizers should not cause any problems in the end product detergent, should be highly compatible with all the other ingredients of the detergent and, preferably, should even contribute to the washing and cleaning effect. Of the many previously proposed suspension stabilizers, the substantially insoluble nonionic surfactants, optionally containing an inorganic electrolyte, have so far proved to be the most successful in practice, because these stabilizers and the zeolite suspensions stabilized with them show the requisite properties to a high degree. However, in order to optimize the economic position of aqueous zeolite suspensions as compared to zeolite powders in the production of detergents and cleaners, it was desirable to improve the rheological properties of the zeolite suspensions. This guarantees greater flexibility of use, for example through prolonged stability in storage, transportability and universal suitability for use in the different processes used for producing detergents on an industrial scale.